1. Field of the Invention
The present invention relates to impedance matching circuit modules configured to perform impedance matching between an antenna and a high-frequency front end unit, and also relates to impedance matching switch circuit modules included in the impedance matching circuit modules.
2. Description of the Related Art
Wireless communication terminals, such as cellular phones, include an antenna for transmitting/receiving high-frequency signals to/from the outside and a high-frequency front end unit for performing transmission processing and reception processing for high-frequency signals. If impedance matching is not performed between the antenna and high-frequency front end unit in the frequency band of transmitted/received high-frequency signals, the high-frequency signals cannot be transmitted between the antenna and the high-frequency front end unit with a low loss. Thus, in general, an impedance matching circuit is arranged between the antenna and the high-frequency front end unit. In other words, the antenna is connected to the front end unit through the impedance matching circuit.
In recent years, the frequency band of an antenna and a high-frequency front end unit has been increasingly widened and the antenna and the high-frequency front end unit are capable of supporting a plurality of bands (communication frequency bands) within this wide frequency band. However, an impedance matching circuit defined by a fixed circuit pattern including only inductors and capacitors allows impedance matching to be performed in a limited frequency band and, thus, it is not easy to achieve low-loss transmission of high-frequency signals in the above-described plurality of bands.
Accordingly, in the high-frequency module (referred to as an antenna device in Japanese Unexamined Patent Application Publication No. 2003-179426) disclosed in Japanese Unexamined Patent Application Publication No. 2003-179426, an LC resonant circuit is connected to or disconnected from an antenna in accordance with a transmission/reception band, and low-loss transmission of high-frequency signals in two different bands is realized by selectively using this LC resonant circuit.
However, in the high-frequency module disclosed in Japanese Unexamined Patent Application Publication No. 2003-179426, widening of a band cannot be achieved by using a single LC resonant circuit since there is an influence from the band pass characteristics of the LC resonant circuit. Thus, when the frequency bands are spaced apart from each other, an LC resonant circuit needs to be provided for each of the bands in which the antenna and the front end unit perform transmission and reception. The number of switching terminals varies in accordance with the number of the LC resonant circuits. Thus, when the number of utilized bands is increased due to widening of a band (wider frequency band), the number of the LC resonant circuits and the number of the switching terminals of the switches are increased, which results in an increase in the size of the high-frequency module. In other words, it is not easy to reduce a device size while still supporting a wide band. Further, the circuit constants of the LC circuit need to be adjusted in accordance with the utilized band whenever the utilized band changes and, thus, the specifications of the switch need to be changed, making it difficult to change the design.